Recently, importance of repulping techniques for preparing reclaimed papers from used papers has been increased because of finite forest resources.
Adhesive papers coated with adhesives are sold as memoranda pads and the like. When these adhesive papers are mixed in usual used papers to be reclaimed, various problems caused by their adhesives are aroused in the steps of repulping. In order to solve the problems in the steps of repulping, some suggestions have been made.
Japanese Patent Laid-Open Publication No.74486/1991 discloses adhesive compositions which comprise modified copolymers, hydrogenated rosin and polyethylene glycol, wherein the modified copolymers are obtained by copolymerizing acrylate, .alpha.,.beta.-ethylenic unsaturated dicarboxylic acid and assistant monomers such as vinyl acetate, styrene, methyl methacrylate and the like, subsequently esterifying thus obtained copolymer with nonionic agents, and thereafter, neutralizing with alkali. Of these compositions, the neutralized or esterified parts derived from the unsaturated dicarboxylic acid and the assistant monomers are soluble in water, but the main component derived from acrylate are essentially difficult to dissolve in water. On the account, the adhesive compositions remain without solubilized after repulping by sticking to the used papers or by making granular dispersed particles. These adhesive dispersed particles make trouble in the repulping process because they clog filters on filtrating the residues. Further, the adhesive dispersed particles cause occurrence of tacks on paper making, and have a bad influence on the quality of the product papers.
Japanese Patent Publication No.23294/1974 discloses adhesives composed of copolymers and nonionic surface active agents wherein the copolymers are formed by copolymerization of monomers without carboxyl group such as vinyl ester, acrylate, methacrylate, ethylene, stylene, methyl vinyl ether, vinyl chloride, acrylonitrile, etc. and monomers with carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, aconitic acid, monoalkyl maleic acid, monoalkyl fumaric acid, monoalkyl itaconic acid, etc. The adhesives are not suitable from the viewpoint of repulping since they also have water-insoluble parts like those described above.
Japanese Patent Laid-Open Publication No. 33926/1977 disclose adhesives obtained by adding water soluble plasticizers to copolymers of polymerizable vinyl monomers having carboxyl group and basic monomers. To the adhesives, water soluble plasticizers such as polyvalent alcohol, polyetherpolyol, polypropylene glycol and the like are added in order to acquire capability of water solubility for repulping. However, these water soluble plasticizers are apt to cause bleeding when the adhesives are applied to base papers. Further, on bonding adhesive tapes to paper products, the water soluble plasticizers of the adhesives are transferred to papers and are apt to arouse problems of paper contaminations.
Furthermore, U.S. Pat. No. 3,865,770 discloses adhesives which are obtained by neutralizing copolymers of acrylates and vinyl carboxylic acids with alkanolamines.